Currently looking at a //e mobo that doesn't want to boot from a disk. I've tried both Disk II and DuoDisk controllers and drives (both work on "good" //e) so I think there's a mobo problem and just started digging into that. But I've got no knowledge of how the mobo factors into the boot process (other than expecting it easily could)
I pulled and verified the CD and EF ROMs are fine. I can't comment on RAM because I haven't been able to get anything to load. The asciiexpress.net loader I thought could load app to RAM and run, but the "non-format" version appears to be loading the disk writer which does crash so I'm expecting that's because of some disk error. I checked the signals on the drive controller and what I've noticed is the head calibration sequencing of O0, O1, O2, O3 is happening and after the period of that sequence O0 does go high and it looks like there's data being read from the disk. AFAIK the sequencing of pulsing the stepper for calibration is a ROM function and ROMs verified. So where should I look next?
I think the SAMS book IDs 4 suspect but I didn't start probing the board drive board volatages, the ICs would be my firs suspects. I think two are the bi-directional data muxes and don't have an easy to check those. I did start wiring up an arduino so I can write some tests for the ICs. I've done this testing manually after plugging in my TJBoldt ProDOS cards backwards and frying a 74245 but that's a story for another day.... I think it's best to automate logic tests if I'm needing to do that again.
I've attached the logic capture, please note O3 is correct, the lead had just come loose and that's why it's flat it was working correctly.